Impact-resistant polyolefin compositions

ABSTRACT

Polyolefin compositions comprising (percent by weight): 1) 55-80% of a crystalline propylene homopolymer or copolymer containing up to 15% of ethylene and/or C 4 -C 10  α-olefin(s) and having an MFR value of at least 15 g/10 min, and 2) 2) 20-45 wt % of a copolymer of ethylene with one or more C 4 -C 10  α-olefin(s) containing from 10 to 4 wt % of said C 4 -C 10  α-olefin(s). The said compositions have values of MFR equal to or higher than 15 g/10 min, a total content of ethylene of 20% or more, a total content of C 4 -C 10  α-olefin(s) of 4.5% or more, a ratio of the total content of ethylene to the total content of C 4 -C 10  α-olefin(s) of 2.3 or more, and an intrinsic viscosity value of the fraction soluble in xylene at room temperature of 1.7 dl/g or less.

This application is the U.S. national phase of International ApplicationPCT/EP2003/006097, filed Jun. 11, 2003.

The present invention concerns polyolefin compositions comprising acrystalline propylene polymer component selected from propylene-ethyleneand/or other α-olefin random copolymers, and a copolymer of ethylenewith C₄-C₁₀ α-olefins.

The compositions of the present invention can be easily converted intovarious kinds of finished or semi-finished articles, in particular byusing injection-molding techniques, as they exhibit relatively highvalues of melt flow rate (MFR). In addition, as they show substantiallyno stress whitening when bending a 1 mm thick plaque, the saidcompositions can be used for several applications, including toys andhousewares, in particular for those articles that need with impactresistance at low temperatures without failure of the articles. The saidarticles can advantageously be used in the food-contact applications,examples of which are food containers suitable for freezers.

Compositions comprising polypropylene and a rubbery phase formed by anelastomeric copolymer of ethylene with α-olefins are already known inthe art, and described in particular in European patents 170 255 and 373660, and in WO 01/19915. Said compositions exhibit impact resistanceand, in the case of European patent 373 660 and WO 01/19915,transparency values interesting for many applications, however theoverall balance of properties is still not totally satisfactory in thewhole range of possible applications, in view of the high standardsrequired by the market. Therefore there is a continuous demand forcompositions of this kind with improved properties.

A new and valuable balance of properties has now been achieved by thepolyolefin compositions of the present invention, comprising (percent byweight):

-   1) 55-80% of a crystalline propylene homopolymer or copolymer    containing up to 15% of ethylene and/or C₄-C₁₀ α-olefin(s) and    having an MFR value of at least 15 g/10 min; and-   2) 20-45% of a copolymer of ethylene with one or more C₄-C₁₀    α-olefin(s) containing from 10 to 40% of said C₄-C₁₀ α-olefin(s);    said compositions having values of MFR (230° C., 2.16 kg) equal to    or higher than 15 g/10 min, a total content of ethylene of 20% or    more, a total content of C₄-C₁₀ α-olefin(s) of 4.5% or more, a ratio    of the total content of ethylene to the total content of C₄-C₁₀    α-olefin(s) of 2.3 or more, and an intrinsic viscosity value of the    fraction soluble in xylene at room temperature of 1.7 dl/g or less,    preferably of 1.5 dl/g or less.

From the above definitions it is evident that the term “copolymer”includes polymers containing more than one kind of comonomers.

The compositions of the present invention provide in particular acombination of very high flowability and high impact resistance (interms of ductile/brittle transition temperature and Izod impactresistance) and high transparency.

The preferred polyolefin compositions are flexible polyolefincompositions comprising (percent by weight):

-   1) 55-75%, preferably 55-70%, of a crystalline propylene homopolymer    or copolymer containing up to 15% of ethylene and/or C₄-C₁₀    α-olefin(s) and having a MFR from 15 to 80 g/10 min; and-   2) 25-45%, preferably 30-45%, of a copolymer of ethylene with one or    more C₄-C₁₀ α-olefin(s) containing from 15 to 40% of said C₄-C₁₀    α-olefin(s);    said compositions having values of MFR (230° C., 2.16 kg) equal to    or higher than 15 g/10 min, a total content of ethylene of 20% or    more, a total content of C₄-C₁₀ α-olefin(s) of 6% or more, a ratio    of the total content of ethylene to the total content of C₄-C₁₀    α-olefin(s) of 2.3 or more, a total fraction soluble in xylene at    room temperature of 18 wt % or higher, preferably at least 20 wt %,    and an intrinsic viscosity value of the fraction soluble in xylene    at room temperature of 1.7 dl/g or less, preferably of 1.5 dl/g or    less.

The compositions of the present invention have preferably a MFR valuefrom 15 g/10 to 40 g/10 min.

Particularly preferred features for the compositions of the presentinvention are:

-   -   content of fraction insoluble in xylene at room temperature (23°        C.) (substantially equivalent to the Isotacticity Index) for        component 1): not less than 90%, in particular not less than        93%, said percentages being by weight and referred to the weight        of component 1);    -   a total content of ethylene from 20% to 40% by weight;    -   a total content of C₄-C₁₀ α-olefin(s) from 6% to 15% by weight;    -   a flexural modulus value less than 770 MPa, but preferably        higher than 600 MPa, more preferably higher than 650 MPa;    -   fraction soluble in xylene at room temperature: less than 35%,        more preferably less than 30% by weight;    -   intrinsic viscosity of the fraction soluble in xylene at room        temperature in the range from 0.8 to 1.5 dl/g.

The ductile/brittle transition temperature is generally equal to orlower than 35° C., the lower limit being indicatively of about 60° C.

The said C₄-C₁₀ α-olefins, which are or may be present as comonomers inthe components and fractions of the compositions of the presentinvention, are represented by the formula CH₂═CHR, wherein R is an alkylradical, linear or branched, with 2-8 carbon atoms or an aryl (inparticular phenyl) radical.

Examples of said C₄-C₁₀ α-olefins are 1-butene, 1-pentene, 1-hexene,4-methyl-1-pentene and 1-octene. Particularly preferred is 1-butene.

The compositions of the present invention can be prepared by asequential polymerization, comprising at least two sequential steps,wherein components 1) and 2) are prepared in separate subsequent steps,operating in each step, except the first step, in the presence of thepolymer formed and the catalyst used in the preceding step. The catalystis added only in the first step, however its activity is such that it isstill active for all the subsequent steps.

Preferably component 1) is prepared before component 2).

The polymerization, which can be continuous or batch, is carried outfollowing known techniques and operating in liquid phase, in thepresence or not of inert diluent, or in gas phase, or by mixedliquid-gas techniques. Preferably both components 1) and 2) are preparedin gas phase.

Reaction time, pressure and temperature relative to the two steps arenot critical, however it is best if the temperature is from 20 to 100°C. The pressure can be atmospheric or higher.

The regulation of the molecular weight is carried out by using knownregulators, hydrogen in particular.

Such polymerization is preferably carried out in the presence ofstereospecific Ziegler-Natta catalysts. An essential component of saidcatalysts is a solid catalyst component comprising a titanium compoundhaving at least one titanium-halogen bond, and an electron-donorcompound, both supported on a magnesium halide in active form. Anotheressential component (co-catalyst) is an organoaluminum compound, such asan aluminum alkyl compound.

An external donor is optionally added.

The catalysts generally used in the process of the invention are capableof producing polypropylene with an isotactic index greater than 90%,preferably greater than 95%. Catalysts having the above mentionedcharacteristics are well known in the patent literature; particularlyadvantageous are the catalysts described in U.S. Pat. No. 4,399,054 andEuropean patent 45977.

The solid catalyst components used in said catalysts comprise, aselectron-donors (internal donors), compounds selected from the groupconsisting of ethers, ketones, lactones, compounds containing N, Pand/or S atoms, and esters of mono- and dicarboxylic acids.

Particularly suitable electron-donor compounds are phthalic acid esters,such as diisobutyl, dioctyl, diphenyl and benzylbutyl phthalate.

Other electron-donors particularly suitable are 1,3-diethers of formula:

wherein R^(I) and R^(II) are the same or different and are C₁-C₁₈ alkyl,C₃-C₁₈ cycloalkyl or C₇-C₁₈ aryl radicals; R^(III) and R^(IV) are thesame or different and are C₁-C₄ alkyl radicals; or are the 1,3-diethersin which the carbon atom in position 2 belongs to a cyclic or polycyclicstructure made up of 5, 6 or 7 carbon atoms and containing two or threeunsaturations.

Ethers of this type are described in published European patentapplications 361493 and 728769.

Representative examples of said dieters are2-methyl-2-isopropyl-1,3-dimethoxypropane,2,2-diisobutyl-1,3-dimethoxypropane,2-isopropyl-2-cyclopentyl-1,3-dimethoxypropane,2-isopropyl-2-isoamyl-1,3-dimethoxypropane, 9,9-bis (methoxymethyl)fluorene.

The preparation of the above mentioned catalyst components is carriedout according to various methods.

For example, a MgCl₂.nROH adduct (in particular in the form ofspheroidal particles) wherein n is generally from 1 to 3 and ROH isethanol, butanol or isobutanol, is reacted with an excess of TiCl₄containing the electron-donor compound. The reaction temperature isgenerally from 80 to 120° C. The solid is then isolated and reacted oncemore with TiCl₄, in the presence or absence of the electron-donorcompound, after which it is separated and washed with aliquots of ahydrocarbon until all chlorine ions have disappeared.

In the solid catalyst component the titanium compound, expressed as Ti,is generally present in an amount from 0.5 to 10% by weight. Thequantity of electron-donor compound which remains fixed on the solidcatalyst component generally is 5 to 20% by moles with respect to themagnesium dihalide.

The titanium compounds which can be used for the preparation of thesolid catalyst component are the halides and the halogen alcoholates oftitanium. Titanium tetrachloride is the preferred compound.

The reactions described above result in the formation of a magnesiumhalide in active form. Other reactions are known in the literature,which cause the formation of magnesium halide in active form startingfrom magnesium compounds other than halides, such as magnesiumcarboxylates.

The Al-alkyl compounds used as co-catalysts comprise the Al-trialkyls,such as Al-triethyl, Al-triisobutyl, Al-tri-n-butyl, and linear orcyclic Al-alkyl compounds containing two or more Al atoms bonded to eachother by way of O or N atoms, or SO₄ or SO₃ groups. The Al-alkylcompound is generally used in such a quantity that the Al/Ti ratio befrom 1 to 1000.

The electron-donor compounds that can be used as external donors includearomatic acid esters such as alkyl benzoates, and in particular siliconcompounds containing at least one Si—OR bond, where R is a hydrocarbonradical. Examples of silicon compounds are (tert-butyl)₂Si(OCH₃)₂,(cyclohexyl)(methyl)Si(OCH₃)₂, (phenyl)₂Si(OCH₃)₂ and(cyclopentyl)₂Si(OCH₃)₂. 1,3-diethers having the formulae describedabove can also be used advantageously. If the internal donor is one ofthese dieters, the external donors can be omitted.

The catalysts can be pre-contacted with small amounts of olefins(prepolymerization).

Other catalysts that may be used in the process according to the presentinvention are metallocene-type catalysts, as described in U.S. Pat. No.5,324,800 and EP-A-0 129 368; particularly advantageous are bridgedbis-indenyl metallocenes, for instance as described in U.S. Pat. No.5,145,819 and EP-A-0 485 823. Another class of suitable catalysts arethe so-called constrained geometry catalysts, as described in EP-A-0 416815 (Dow), EP-A-0 420 436 (Exxon), EP-A-0 671 404, EP-A-0 643 066 and WO91/04257. These metallocene compounds may be used in particular toproduce the copolymers (a) and (b).

The compositions of the present invention can also be obtained bypreparing separately the said components 1) and 2), by operating withthe same catalysts and substantially under the same polymerizationconditions as previously explained (except that a wholly sequentialpolymerization process will not be carried out, but the said componentswill be prepared in separate polymerization steps) and then mechanicallyblending said components in the molten or softened state. Conventionalmixing apparatuses, like screw extrudres, in particular twin screwextruders, can be used.

The compositions of the present invention can also contain additivescommonly employed in the art, such as antioxidants, light stabilizers,heat stabilizers, nucleating agents, colorants and fillers.

In particular, the addition of nucleating agents brings about aconsiderable improvement in important physical-mechanical properties,such as flexural modulus, Heat Distortion Temperature (HDT), tensilestrength at yield and transparency.

Typical examples of nucleating agents are the p-tert-butyl benzoate andthe 1,3- and 2,4-dibenzylidenesorbitols.

The nucleating agents are preferably added to the compositions of thepresent invention in quantities ranging from 0.05 to 2% by weight, morepreferably from 0.1 to 1% by weight with respect to the total weight.

The addition of inorganic fillers, such as talc, calcium carbonate andmineral fibers, also brings about an improvement to some mechanicalproperties, such as flexural modulus and HDT. Talc can also have anucleating effect.

The particulars are given in the following examples, which are given toillustrate, without limiting, the present invention.

EXAMPLES 1-3

In the following examples polyolefin compositions according to thepresent invention are prepared by sequential polymerization.

The solid catalyst component used in polymerization is a highlystereospecific Ziegler-Natta catalyst component supported on magnesiumchloride, containing about 2.5% by weight of titanium anddiisobutylphthalate as internal donor, prepared by analogy with themethod described in Example 1 of European published patent application674991.

Catalyst System and Prepolymerization Treatment

Before introducing it into the polymerization reactors, the solidcatalyst component described above is contacted at −5° C. for 5 minuteswith aluminum triethyl (TEAL) and dicyclopentyldimethoxysilane (DCPMS),in a TEAL/DCPMS weight ratio equal to about 4 and in such quantity thatthe TEAL/Ti molar ratio be equal to 65.

The catalyst system is then subjected to prepolymerization bymaintaining it in suspension in liquid propylene at 20° C. for about 20minutes before introducing it into the first polymerization reactor.

Polymerization

The polymerization is carried out in continuous in a series of two gasphase reactors equipped with devices for the transfer of the productcoming from the reactor immediately preceding to the one immediatelyfollowing.

In gas phase the hydrogen and the monomer(s) are analyzed in continuousand fed in such a manner that the desired concentration be maintainedconstant.

Into a first gas phase polymerization reactor a propylene/ethylenecopolymer is produced by feeding in a continuous and constant flow theprepolymerized catalyst system, hydrogen (used as molecular weightregulator) and propylene and ethylene monomers in the gas state, thusobtaining component 1).

The polymer produced in the first reactor is discharged in the secondreactor where an ethylene/butene copolymer is produced by feeding themonomer(s) and hydrogen in proper molar ratios, thus obtaining component2).

Then the polymer particles are introduced in a rotating drum, where theyare mixed with 0.05% by weight of paraffinic oil, 0.05% by weight ofsodium stearate, 0.15% by weight of Irganox® B215 (1 weight part ofpentaerithryl-tetrakis[3(3,5-di-tert-butyl-4-hydroxyphenyl] mixed with 1weight part of tris(2,4-ditert-butylphenyl) phosphite) and 0.2% byweight of Millad® 3988 3,4-dimethylbenzylidene sorbitol.

Then the polymer particles are introduced in a twin screw extruderBerstorff™ ZE 25 (length/diameter ratio of screws: 33) and extrudedunder nitrogen atmosphere in the following conditions:

-   Rotation speed: 250 rpm;-   Extruder output: 6-20 kg/hour;-   Melt temperature: 200-250° C.

The data relating to the final polymer compositions reported in table 1and 2 are obtained from measurements carried out on the so extrudedpolymers.

The data shown in the tables are obtained by using the following testmethods.

Molar Ratios of the Feed Gases

Determined by gas-chromatography.

Ethylene and 1-butene Content of the Polymers

Determined by I.R. spectroscopy

Melt Flow Rate (MFR)

Determined according to ASTM D 1238, condition L (MFR“L”).

Xylene Soluble and Insoluble Fractions

Determined as follows.

2.5 g of polymer and 250 ml of xylene are introduced in a glass flaskequipped with a refrigerator and a magnetical stirrer. The temperatureis raised in 30 minutes up to the boiling point of the solvent. The soobtained clear solution is then kept under reflux and stirring forfurther 30 minutes. The closed flask is then kept for 30 minutes in abath of ice and water and in thermostatic water bath at 25° C. for 30minutes as well. The so formed solid is filtered on quick filteringpaper. 100 ml of the filtered liquid is poured in a previously weighedaluminum container which is heated on a heating plate under nitrogenflow, to remove the solvent by evaporation. The container is then keptin an oven at 80° C. under vacuum until constant weight is obtained. Theweight percentage of polymer soluble in xylene at room temperature isthen calculated. The percent by weight of polymer insoluble in xylene atroom temperature is considered the Isotacticity Index of the polymer.This value corresponds substantially to the Isotacticity Indexdetermined by extraction with boiling n-heptane, which by definitionconstitutes the Isotacticity Index of polypropylene.

Intrinsic Viscosity (I.V.)

Determined in tetrahydronaphthalene at 135° C.

Flexural Modulus

Determined according to ISO 178.

Ductile/Brittle Transition Temperature (D/B)

Determined according to internal method MA 17324, available uponrequest. According to this method, the bi-axial impact resistance isdetermined through impact with an automatic, computerised strikinghammer. The circular test specimens are obtained by cutting withcircular hand punch (38 mm diameter). They are conditioned for at least12 hours at 23° C. and 50 RH and then placed in a thermostatic bath attesting temperature for 1 hour.

The force-time curve is detected during impact of a striking hammer (5.3kg, hemispheric punch with a 1.27 cm diameter) on a circular specimenresting on a ring support. The machine used is a CEAST 6758/000 typemodel No. 2.

D/B transition temperature means the temperature at which 50% of thesamples undergoes fragile break when submitted to the said impact test.

Preparation of the Plaque Specimens

Plaques for D/B measurement, having dimensions of 127×127×1.5 mm areprepared according to internal method MA 17283; plaques for hazemeasurement, 1 mm thick, are prepared by injection moulding according tointernal method MA 17335 with injection time of 1 second, temperature of230° C., mould temperature of 40° C., description of all the saidmethods being available upon request.

Method MA 17283

The injection press is a Negri Bossi™ type (NB 90) with a clamping forceof 90 tons.

The mould is a rectangular plaque (127×127×1.5 mm).

The main process parameters are reported below:

-   Back pressure (bar): 20-   Injection time (s): 3-   Maximum Injection pressure (MPa): 14-   Hydraulic injection pressure (MPa): 6-3-   First holding hydraulic pressure (MPa): 4±2-   First holding time (s): 3-   Second holding hydraulic pressure (MPa): 3±2-   Second holding time (s): 7-   Cooling time (s): 20-   Mould temperature (° C.): 60-   The melt temperature is between 220 and 280° C.    Method MA 17335

The injection press is a Battenfeld™ type BA 500CD with a clamping forceof 50 tons. The insert mould leads to the moulding of two plaques(55×60×1 or 1.5 mm each).

Haze on Plague

Determined according to internal method MA 17270, available uponrequest.

The plaques are conditioned for 12 to 48 hours at relative humidity of50±5% and temperature of 23±1° C.

The apparatus used is a Hunter™ D25P-9 calorimeter. The measurement andcomputation principle are given in the norm ASTM-D1003.

The apparatus is calibrated without specimen, the calibration is checkedwith a haze standard. The haze measurement is carried out on fiveplaques.

Izod Impact Strength (Notched)

Determined according to ISO 180/1A.

COMPARATIVE EXAMPLE 1C

Example 1 is repeated except that the polymerisation is carried out in aseries of three reactors. Into the first reactor a crystallinepropylene-ethylene copolymer is produced feeding the monomers andhydrogen in proper molar ratios (component (A′)). The copolymer thusproduced is discharged into the second reactor where apropylene-ethylene copolymer is produced by feeding the monomers andhydrogen in proper molar ratios (component (A″)).

The copolymer produced in the second reactor is discharged in acontinuous flow and, after having being purged of unreacted monomers, isintroduced in a continuous flow into the third gas phase reactor,together with quantitatively constant flows of hydrogen and ethylene and1-butene monomers in the gas state. Component (B) is thus obtained.

Polymerisation conditions, molar ratios, composition and properties ofthe copolymers obtained are shown in table 2. The comparativecomposition shows a value of flexural modulus in the same range as theone of the compositions of the present invention, value which isobtained only thanks to a crystalline polymer moiety of the matrixhaving a low flowability.

In comparison with the comparative composition, the compositionsaccording to the present invention have a comparable or even betterstiffness and better impact resistance in terms of ductile/brittletransition temperature in spite of remarkably higher MFR values thatimprove workability as it generally affects stiffness and impactresistance.

TABLE 1 Example and comparative example 1 2 3 1c 1^(st) Gas PhaseReactor-crystalline propylene-ethylene copolymer Temperature ° C. 80 8080 80 Pressure MPa — — — 1.8 H₂/C₃ ⁻ mol — — — 0.002 C₂ ⁻/(C₂ ⁻ + C₃ ⁻)mol — — — 0.019 MFR “L” g/10′ 41 52 24.4 1.2 Ethylene content in thecopolymer wt % 2.1 2.0 2.4 2.6 Xylene soluble fraction wt % 3.6 — 4.1 —Split wt % 66 68 69 39 2^(nd) Gas Phase Reactor-crystallinepropylene-ethylene copolymer Split wt % 0 0 0 39 MFR “L” (total) g/10′ —— — 11.7 Ethylene content in the copolymer wt % — — — 2.6 H₂/C₃ ⁻ mol —— — 0.419 Xylene-soluble fraction (total) wt % — — — 96.5 2^(nd)/3^(rd)Gas Phase Reactor-ethylene-butene-1 copolymer rubber Temperature ° C. 7575 70 70 Pressure MPa — — — 1.6 H₂/C₂ ⁻ mol — 0.466 C₄ ⁻/(C₄ ⁻ + C₂ ⁻)mol 0.55 0.55 0.51 0.35 Split wt % 34 32 31 22 Butene-1 in the rubber wt% 27 24 25.8 23.6 Xylene soluble fraction wt % 65 60 64 — Notes to thetable. Split = weight fraction of polymer produced in the specifiedreactor; C₂ ⁻ = ethylene; C₄ ⁻ = butene; H₂/C₂ ⁻ = molar ratio of fedhydrogen to fed ethylene; C₂ ⁻/(C₂ ⁻ + C₃ ⁻) = molar ratio of fedethylene to fed ethylene plus fed propylene; C₄ ⁻/(C₄ ⁻ + C₂ ⁻) = molarratio of fed butene to fed butene plus fed ethylene.

TABLE 2 Example and comparative example 1 2 3 1c MFR “L” g/10′ 32.5 28.219.4   9.4  Xylene-soluble fraction wt % 24.6 — 22.6  13.6  I.V. ofxylene-soluble fraction dl/g 1.05 — 1.09   1.29 Ethylene content wt %26.0 25.7 25.4  18.4  Butene-1 content wt % 9.1 7.7 8.0   5.2  Flexuralmodulus MPa 671 757 760 1015 D/B transition temperature ° C. −53 −49 −50−22 Izod impact resistance kJ/m² — — 37.9 190¹⁾ at 23° C. Haze, 1 mmplaque % 35 39.5 23.7 13.3 ¹⁾Expressed in J/m; 190 J/m corresponds toabout 15.1 kJ/m².

1. Polyolefin compositions comprising (percent by weight): 1) 55-80% ofa crystalline propylene homopolymer or copolymer containing up to 15% ofat least one of ethylene and C₄-C₁₀ α-olefin(s) and having a MFR value(230° C., 2.16 kg) of at least 15 g/10 min; and 2) 20-45% of a copolymerof ethylene with at least one of C₄-C₁₀ α-olefin(s) containing from 10to 40% of said C₄-C₁₀ α-olefin(s); said compositions having MFR (230°C., 2.16 kg) values of at least 15 g/10 min, a total content of ethyleneof 20% or more, a total content of C₄-C₁₀ α-olefin(s) of 4.5% or more, aratio of the total content of ethylene to the total content of C₄-C₁₀α-olefin(s) of 2.3 or more, and an intrinsic viscosity value of afraction soluble in xylene at room temperature of at most 1.7 dl/g. 2.The polyolefin compositions according to claim 1 comprising (percent byweight): 1) 55-75% of a crystalline propylene homopolymer or copolymercontaining up to 15% of at least one of ethylene and C₄-C₁₀ α-olefin(s)and having a MFR from 15 to 80 g/10 min; and 2) 25-45% of a copolymer ofethylene with at least one of C₄-C₁₀ α-olefin(s) containing from 20 to40% of said C₄-C₁₀ α-olefin(s); said compositions having MFR (230° C.,2.16 kg) values at least 15 g/10 min, a total content of ethylene of 20%or more, a total content of C₄-C₁₀ α-olefin(s) of 6% or more, a ratio ofthe total content of ethylene to the total content of C₄-C₁₀ α-olefin(s)of 2.3 or more, a total fraction soluble in xylene at room temperatureof 18 wt % or higher, and an intrinsic viscosity value of the fractionsoluble in xylene at room temperature of at most 1.7 dl/g.
 3. Thepolyolefin compositions of claim 1, having MFR values of at least 30g/10 min.
 4. The polyolefin compositions of claim 1, wherein theintrinsic viscosity of the fraction soluble in xylene at roomtemperature is in the range from 0.8 to 1.5 dl/g.
 5. The polyolefincompositions of claim 1, wherein the fraction soluble in xylene at roomtemperature is higher than 20%.
 6. The polyolefin compositions of claim1, having a ductile/brittle transition temperature of at most −35° C. 7.A process for producing polyolefin compositions, which comprise: 1)55-80% of a crystalline propylene homopolymer or copolymer containing upto 15% of at least one of ethylene and C₄-C₁₀ α-olefin(s) and having aMFR value (230° C., 2.16 kg) of at least 15 g/10 min; and 2) 20-45% of acopolymer of ethylene with at least one of C₄-C₁₀ α-olefin(s) containingfrom 10 to 40% of said C₄-C₁₀ α-olefin(s); said compositions having MFR(230° C., 2.16 kg) values at least 15 g/10 min, a total content ofethylene of 20% or more a total content of C₄-C₁₀ α-olefin(s) of 4.5% ormore, a ratio of the total content of ethylene to the total content ofC₄-C₁₀ α-olefin(s) of 2.3 or more, and an intrinsic viscosity value of afraction soluble in xylene at room temperature of at most 1.7 dl/g, theprocess being carried out in at least two sequential steps, wherein inat least one polymerization step the relevant monomer(s) are polymenzedto form component 1) and in the other step the relevant monomers arepolymerized to form component 2), operating in each step, except thefirst step, in the presence of the polymer formed and the catalyst usedin the preceding step.
 8. The process of claim 7, wherein thepolymerization catalyst is a stereospecific Ziegler-Natta catalystcomprising, as catalyst-forming components, a solid component comprisinga titanium compound having at least one titanium-halogen bond and anelectron-donor compound, both supported on a magnesium halide in activeform, and an organoaluminum compound.
 9. The process of claim 7, whereinboth components 1) and 2) are prepared in gas phase.
 10. Injectionmoulded articles comprising polyolefin compositions, which comprise: 1)55-80% of a crystalline propylene homopolymer or copolymer containing upto 15% at least one of ethylene and C₄-C₁₀ α-olefin(s) and having a MFRvalue (230° C., 2.16 kg) of at least 15 g/10 min; and 2) 20-45% of acopolymer of ethylene with at least one of C₄-C₁₀ α-olefin(s) containingfrom 10 to 40% of said C₄-C₁₀ α-olefin(s); said compositions having MFR(230° C., 2.16 kg) values at least 15 g/10 min, a total content ofethylene of 20% or more, a total content of C₄-C₁₀ α-olefin(s) of 4.5%or more, a ratio of the total content of ethylene to the total contentof C₄-C₁₀ α-olefin(s) of 2.3 or more, and an intrinsic viscosity valueof a fraction soluble in xylene at room temperature of at most 1.7 dl/g.11. The polyolefin compositions according to claim 2 comprising (percentby weight): 1) 55-70% of a crystalline propylene homopolymer orcopolymer containing up to 15% of at least one of ethylene and C₄-C₁₀α-olefin(s) and having a MFR value of from 15 to 80 g/10 min; and 2)30-45% of a copolymer of ethylene with at least one of C₄-C₁₀α-olefin(s) containing from 20 to 40% of said C₄-C₁₀ α-olefin(s); saidcompositions having values of MFR (230° C., 2.16 kg) equal to or higherthan 15 g/10 min, a total content of ethylene of 20% or more, a totalcontent of C₄-C₁₀ α-olefin(s) of 6% or more, a ratio of the totalcontent of ethylene to the total content of C₄-C₁₀ α-olefin(s) of 2.3 ormore, a total fraction soluble in xylene at room temperature of 18 wt %or higher, and an intrinsic viscosity value of a fraction soluble inxylene at room temperature of at most 1.7 dl/g.